In medicine a frequent problem is to generate time-resolved, three-dimensional images of dynamic (time-dependent) events within objects which vary with time, from recordings of projections of the objects taken from different directions. The object to be imaged can be the human body, for eV(ample. Here, in particular, the spread of contrast agents in vessels, for eV(ample dynamic angiography, in tissue, for eV(ample perfusion, the spontaneous movement of organs, for eV(ample the heartbeat, breathing, peristalsis or swallowing, or eV(ternal mechanical compression of tissue (elastography), can be considered as dynamic events. The recordings can be made with X-ray apparatus with a flat detector, as described for eV(ample in US 2006/0120507 A1.
Such a known X-ray diagnostic apparatus is illustrated in FIG. 1. As an imaging unit the X-ray diagnostic apparatus has a C-arm 2 supported in a rotatable manner on a stand 1, an X-ray source, for eV(ample an X-ray emitter 3 and an X-ray image detector 4, these being mounted on the ends of said C-arm.
The X-ray image detector 4 can be a rectangular or square flat semiconductor detector that is preferably made from amorphous silicon (aSi).
A patient support table 5 for imaging the heart of a patient to be eV(amined, for eV(ample, is located in the beam path of the X-ray source 3. An imaging system 6 which receives the image signals from the X-ray image detector 4 and generates a three-dimensional reconstruction of the object to be mapped, is connected to the X-ray diagnostic apparatus. The imaging results can then be viewed on a monitor 7.
Until now, computed tomography (CT) has been employed for time-resolved three-dimensional images of dynamic events. It permits—firstly for static objects—a more or less eV(act three-dimensional reconstruction of the internal parts of the body, since it records projections of the object to be imaged from virtually all directions; typically from a circular orbit of the tube and detector around the patient, as described in Zellerhoff et al. [1]. For dynamically moving objects, periodically repeated CT scans are mostly used, as in Lauritsch et al. [2], in order to record the object to be imaged at different time intervals. The achievable time resolution is then determined by the time required for an individual CT scan and in many cases is inadequate for rapid movements, for eV(ample the heart or the flow of a contrast agent. Cardiac imaging and also perfusion imaging are available with CT. Perfusion imaging with CT is generally limited to a relatively thin layer.
Time-related high-resolution cardiac imaging is also possible with ultrasonic devices. The elastographic method is also technically feasible in the field of ultrasonic imaging.